enzymes Flashcards
Enzymes
Protein catalysts
are not consumed in reactions (catalysts speed up reactions and lower activation energy)
Non-biological reactions use heat as catalyst
Since proteins denature in high heat, enzymes are needed instead
Each enzyme has an optimal temp. and pH to function within
Enzymes attach to substrates (reactants) in specific configurations
So… enzymes decrease the potential energy of transition state molecules, allow a greater proportion of colliding reactants to reach transition state and become products.
the activation energy barrier
Every chemical reaction between molecules involves bond breaking and bond forming
The initial energy needed to start a chemical reaction is called the free energy of activation, or activation energy (EA)
Activation energy is often supplied in the form of heat from the surroundings
How Enzymes Lower the EA Barrier
Enzymes (or catalysts) are biological catalysts that speed up a chemical reaction without being consumed or changing the products of the reaction
Enzymes catalyze reactions by lowering the EA barrier
They do this by allowing the substrates (reactants) to bind and bonds to be broken and made without relying on random collision. (more on this in later slides)
Enzymes do not affect the change in free energy (∆G); instead, they hasten reactions that would occur eventually
Substrate sepcificity of Enzymes
Enzymes have very specific shapes
The substrate binds to a particular site (the active site) on the enzyme to which it is attracted
The reactant that an enzyme acts on is called the enzyme’s substrate
The enzyme binds to its substrate, forming an enzyme-substrate complex
The active site is the region on the enzyme where the substrate binds
Induced fit of a substrate brings chemical groups of the active site into positions that enhance their ability to catalyze the reaction
Catalysis in the Enzyme’s Active Site
In an enzymatic reaction, the substrate binds to the active site of the enzyme
The active site can lower an EA barrier by
Orienting substrates correctly
Straining substrate bonds
Providing a favorable microenvironment
Covalently bonding to the substrate
Induced Fit hypothesis
Substrate binds to active site, forms enzyme-substrate complex
- Functional groups interact which changes the shape of enzyme active site to an induced fit, better accommodates shape of substrate
- Enzyme now stretches and bends bonds that would normally break, but bending lowers the EA
- Once bond breaks, the enzyme’s loses its affinity for the products
- Products are released
How to write an enzyme-catalyzed reaction
enzyme above the arrow
reaction is reversible (some enzymes can do 2 reactions)
Anabolic and catabolic reactions
Anabolism refers to chemical reactions in which simpler substances are combined to form more complex molecules.
usually require energy.
build new molecules and/or store energy.
Catabolism refers to chemical reactions that result in the breakdown of more complex organic molecules into simpler substances.
usually release energy that is used to drive chemical reactions.
factors affecting ezyme activity
- anzyme concentration and substrate concentration
- temperature and pH
- Enzyme activators and inhibitors
Enzyme and Substrate concentration
- enzyme concentration increases, the rate of reaction increases
- as substrate concentration increases, rate of reaction will increase to a point, then plateau/stabilize
- this is because saturation level is max rate of reactions, all the enzymes have a substrate to work on
Temperture and pH
as temperature rises, more interactions occur between the substrates and the enzymes, therefore more reactions occur BUT
when temperature reaches a high enough temperature, the protein can change shape (be denatured)…this would change the shape of the active site and no substrate would be able to enter
each enzyme has an optimal temperature (dependent on the organism…human enzymes prefer 37 C)
each enzyme has an optimal pH…variance from this pH changes the protein shape and extreme pH will denature them
competitive inhibition
Substance called inhibitor competes with the substrate for the enzyme’s active site (looks like substrate)
Enzyme cannot perform
Inhibition is reversible if the substrate’s concentration is increased over the competitor’s
non-competitive inhibition
Inhibitor attaches to a different spot on enzyme, allosteric site
This changes enzymes shape – loses affinity for substrate
allozteric regulation
Cells can further control enzyme activity by:
Restricting the production of the enzyme
Inhibiting the action of the enzyme
Some enzymes have allosteric sites where a substance bonds, and can inhibit (inhibitor) or stimulate (activator).
activators
Cofactors - Often metals which are essential for key components of chemical pathways
Coenzymes - Organic factors, often derived from water-soluble vitamins
allosteric regulation
may either inhibit or stimulate an enzyme’s activity
Allosteric regulation occurs when a regulatory molecule binds to a protein at one site and affects the protein’s function at another site
controlling enzymes: feedback inhibition
Method of control where a product formed later in a chain of reaction returns to the beginning to allosterically inhibit an earlier enzyme
The affect is reduced production of the inhibitor (final product)
Eventually, all inhibitor product disappears, terminating inhibition and reactions begin again as enzyme takes active form
Overall effect: amount of product is tightly controlled
feedback inhibition and metabolic pathways
Cells use feedback inhibition to control metabolic pathways involving a series of sequential reactions, each catalyzed by a specific enzyme
